Binary information transfer device



April 1966 H. J. OGUEY 3,244,901

BINARY INFORMATION TRANSFER DEVICE Filed Feb. 7. 1961 16 Sheets-Sheet 1 7 2 dY/4 S A /Z::) I V & S 44V is RT E2 7/2 4 FIG 1 I I I j I EASY DIRECTION INVENTOR HENRI J. OGUEY AT RNEY April 5, 1966 H. J. OGUEY 3,244,901

BINARY INFORMATION TRANSFER DEVICE Filed Feb. 7, 1961 16 Sheets-Sheet 2 FIG, 4

April 5, 1966 H. .J. OGUEY BINARY INFORMATION TRANSFER DEVICE 16 Sheets-Sheet 5 Filed Feb. '7, 1961 FiG.7o

FIGGQ FIG] April 5, 1966 J, OGUEY 3,244,901

BINARY INFORMATION TRANSFER DEVICE Filed Feb. 7. 1961 16 Sheets-Sheet 4 (III/mom FIG.8

April 5, 1966 J OGUEY 3,244,901

BINARY INFORMATION TRANSFER DEVICE Filed Feb. '7. 1961 16 Sheets-Sheet 5 FIG.I00

\ FIG. 10c

April 5, 1966 H. J. OGUEY 3,244,901

BINARY INFORMATION TRANSFER DEVICE Filed Feb. '7. 1961 16 Sheets-Sheet 6 EASY DlRECTION April 5, 1966 H. J. OGUEY 3,244,901

BINARY INFORMATION TRANSFER DEVICE Filed Feb. 7, 1961 16 Sheets-Sheet 8 158 139 Fl G. 15

, EASY DIRECTION (*P) A4} t A::-t

FIG.16 t. FIG.17

April 1966 H. J OGUEY 3,244,901

BINARY INFORMATION TRANSFER DE VICE Filed Feb. '7, 1961 16 Sheets-Sheet 9 FIG.200 FIG. 210 FIG. 220 FIG.23CI

F|G.20b FIG.21 b F|G.22b IG. 23b

FlG.2|e F|G.22e FIG. 236

F|G.20f FIG. 21f F|G.22f FlG.23f

April 5, 1966 H. J. OGUEY 3,244,901

BINARY INFORMATION TRANSFER DE VICE Filed Feb. 7, 1961 16 Sheets-Sheet 10 FI 6.240 FIG. 24b F|G.24c FIG.24d

FIG.250 FIG.25b FIG. 25c FIG.25d

KEQ/ Q FIG.260 FIG. 26b FIG.26c FIG.26d

FIG. 270 FIG.27b F |G27c FI G.27d

April 5, 1966 H. J. OGUEY 3,244,901

BINARY INFORMATION TRANSFER DE VICE Filed Feb. 7, 1961 16 Sheets-Sheet 11 YQQ EZ FIG.28C| FIG. 290 FIG. 300 F|G.31c|

FIG. 28b F|G.29b FIG.30b FIG.3.1b

FIG.28C FIG. 29c F|G.30c PIC-3.310

FIG 28d F|G.29d FIG.30d FIG. 31d

FIG. 28s FlG.29e FlG.30e F|G.31e

H. J. OGUEY BINARY INFORMATION TRANSFER DEVICE April 5, 1966 16 Sheets-Sheet 13 Filed Feb. '7, 1961 FIG. 36

FIG. 41

FIG. 42

April 5, 1966 H. J. OGUEY BINARY INFORMATION TRANSFER DEVICE 16 Sheets-Sheet 14 Filed Feb. 7, 1961 FIG. 37

April 5, 1966 H. J. OGUEY 3,244,901

BINARY INFORMATION TRANSFER DEVICE Filed Feb. 7, 1961 16 Sheets-Sheet 15 FIG. 45

April 5, 1966 H. J. OGUEY BINARY INFORMATION TRANSFER DEVICE l6 Sheets-Sheet 16 Filed Feb. 7. 1961 United States Patent 3 244 901 BINARY INFORMATION TRANSFER DEVIKJE Henri J. Oguey, Lake Mohegan, N.Y., assignor to International Business Machines Corporation, New York, N.Y., a corporation of New York Filed Feb. 7, 1961, Ser. No. 87,598 Claims priority, application Switzerland, Feb. 9, 1960, 1,412/ 60 Claims. (Ci. 307-88) This invention relates to a device for transmitting binary information, preferably in electronic digital computers and information processing machines, employing thin magnetic layers as storage and switching elements.

In the endeavor to increase the efliciency of electronic digital computers and information processing machines, in other Words, to accelerate the processing speed and the transmission of information, also to improve the reliability of this equipment, it is necessary, from the technical point of view, to develop elements which operate faster and more reliably. Switching elements of thin magnetic layers have been employed recently; these show promise of great success as far as their application in computer circuits is concerned. Thin magnetic films are layers of magnetic material deposited on a substrate and having a thickness of, for example, 100 to 1000 A. (1 A.=10* cm.), in which certain physical properties not prominent in bulk material can be observed. Although such layers have been known in the sphere of physics for a long time, their application as storage and switching elements in digital computers and information processing machines has not been investigated until quite recently. Although numerous circuits with magnetic elements of bulk materials, for example toroids and transfiuxors of ferrites which have proved themselves in computers and data processing machines, are well known in the art, these proven circuits with elements of bulk material cannot be used in the same manner on elements of thin magnetic films, because of the above mentioned divergent physical properties.

The primary reason for this is that the static and dynamic behavior of thin magnetic layers is determined to an advanced degree by the appearance of a uniaxial preferred direction of the magnetization.

This means that the magnetization of the layer endeavors to adjust itself parallel to a definite preferred direction. It is customary to designate this preferred direction as the easy direction and the direction perpendicular to this in the plane of the layer as the hard direction.

Such a magnetic preferred direction in a thin layer can be produced in a number of ways. A conventional method of producing thin layers consists in the evaporation of metal in a high vacuum. With this process, the preferred direction is achieved in the following manner: The metal alloy, for example, permalloy consisting of 80% nickel and 20% iron is heated in a high vacuum at approximately 10- to 10-' Torr up to a temperature at which the metal evaporates. The metallic vapor then condenses onto a suitably arranged substrate, e.g. glass and there forms a mirror-like metal layer. When condensation takes place in the presence of a static magnetic field parallel to the layer surface, a preferred direction of magnetization is formed in the magnetic layer, which is parallel to the direction of the static magnetic field. The influence of a number of determining factors is considered for the formation of this preferred direction, including the directional ordering of atom pairs, the formation of a fibre structure in the film, i.e. in the layer, the interstitial oxygen atoms, anisotropic mechanical stresses and presumably a number of additional effects.

The uniaxial preferred direction of the magnetization Patented Apr. 5, 1966 is referred to as uniaxial magnetic anisotropy. In a thin magnetic layer in conjunction with the high demagnetization at right angles to the plane of the film and the negligible demagnetization in the plane of the layer, this uniaxial magnetic anisotropy conduces to a switching behavior for the magnetization like that encountered in a single domain structure. This means that the magnetization is aligned in the same direction at all points of the layer. The magnetization can thus be represented by a single vector M. If a thin layer with uniaxial anisotropy is exposed to an external magnetic field H, whose direction does not coincide with the easy direction, the magnetization of the layer turns. If a layer having a single domain-like structure is involved, it is customary to speak of a coherent rotation of the magnetization. In general, this mode of switching-over the magnetization in thin magnetic layers is referred to as rotational switchmg.

The direction the magnetization vector M assumes when an external magnetic field H is supplied, can be determined with the aid of a curve which is called the critical curve in the relevant literature. This critical curve and the procedure for determining the adjustment of the magnetization vector M in the presence of an external field H will be dealt with in detail later.

If the external magnetic field H just mentioned is disconnected again, the previously deflected magnetization vector M returns automatically into the first neighboring stable position of equilibrium, which is characterized by a minimum for the energy. Proceeding from the fieldfree condition, this is the easy direction.

Without an external magnetic field there are fundamentally two stable positions of equilibrium, or initial positions, i.e. 0 and with respect to the easy direction, which positions are employed to represent a binary ONE and a binary ZERO, respectively.

The rotation of the magnetization of a thin layer having uniaxial anisotropy is extremely rapid when an external magnetic pulse field is supplied; the switching time is of the order of nanoseconds (l ns=l0 s).

It is known that a suggestion has been made to utilize the rotational switching of thin layers for the transmission of binary information from a first (controlling element) to a second (controlled). The process involves deflecting the magnetization vector in the hard direction (or at least approaching the hard direction) and allowing it to fall back in a position which is decided by a control impulse emanating from the controlling element. This control impulse is obtained by defiectingby the supply of an external field-the magnetization vector of the controlling element out of its easy direction (in which, by virtue of its position, it determines the binary information ONE or ZERO) towards the hard direction. Depending upon whether the magnetization vector of the control element is located, in its initial position, at an angle of 0 or 180 to the easy direction, i.e. whether ONE or ZERO is stored in the element, one obtains an induced positive or negative current impulse in the coupling line between the two elements.

This current impulse generates a magnetic field having a controlling effect on the second element; this influences the switch-back of the magnetization vector which is deflected in the hard direction. According to the polarity of the current impulse, the magnetization vector of the controlled element returns to one of the two possible stable positions in the easy direction and in this way takes over the binary information stored in the first element.

The transmission of binary information employing thin magnetic layers as storage and switching elements has so far only been known for symmetrically coupled transmission devices, for example, shift registers, in which none of the binary information ONE or ZERO is given preference with respect to the other. Hereby, the characteristic of theuniaxial anisotropy of the element is only useful for the switching-over process of the magnetization in the individual elements themselves; the coupling of individual elements is symmetrical, and the existence of a preferred direction in the thin layers is not essential for that. Thus, with respect to the symmetrical coupling properties of the known binary information transfer devices having thin layers with rotational switching, the conditions are similar to those obtaining with information transfer devices having switching elements of bulk magnetic material, eg toroids of ferrite material; such devices also exhibit symmetrical coupling properties.

Accordingly, a prime object of this invention is to 'provide novel devices with asymmetrical coupling properties for transferring binary information from a storage or switching element to a connected, essentially similar storage or switching element.

Another object of this invention is to provide improved shift registers with a direction-dependent preference for the transmission of binary information.

Another object of this invention is to provide novel and improved circuits for the logical connection of binary information.

A further object of the invention is to provide a structure for achieving optimum decoupling between the input and output coupling lines from thin film elements.

Still another object of this invention is to provide improved transfer circuits which achieve the most favorable forward. and backward decoupling possible.

A more specific object of the invention is toprovide an improved circuit and means for transferring a binary 1 and from element to element alternately, thereby ensuring a regeneration of the information to prevent a possible diminution of the signal energy during the course of the shifting process.

Yet another object of this invention is to provide an improved transfer circuit wherein the stray flux couplings between the driver lines generating an external magnetic field and the input and output lines coupling the individual elements is minimized.

It is a feature of this invention that in the information transfer devices herein proposed an external magnetic field can be produced by means of simple line arrangements and simple pulse waveforms; whereby, by appropriate superposition of the external magnetic fields, by switching-in (or out) only one driver current at any one time is required to transfer information from one element to the next independent of synchronization.

The foregoing and other objects, features and advantages of the invention will be apparent from the following more particular description of preferred embodiments of the invention, as illustrated in the accompanying drawings.

The devices embraced by this invention are intended for the transmission of binary information from a controlling magnetic thin film element having an easy direction for the magnetization to a controlled, essentially similar magnetic thin film element, whereby the binary information ONE or ZERO is determined by the direction of the magnetization, and means are visualized for deflecting at the instant of information transfer the magnetization of the controlling magnetic thin film element from a definite initial position by a first magnetic drive field; in general, the fundamental principle here is to visualize coupling means between the magnetic thin film elements, whose effective signal pick-up range with respect to the controlling magnetic thin film element has a maximum value in a direction located obliquely to the direction of the first magnetic drive field and forms an angle with it which, according to its absolute value, is between 15 and 75 degrees. A deviation from the foregoing values, either towards Zero or towards 90", leads to the loss of essential advantages associated with this invention, and which are documented in the examples.

It is possible, from the following description, and with the aid of the attached drawings which illustrate the method, to achieve realization of the invention involved here, whereby attention is drawn to the fact that the arrangements illustrated merely serve to demonstrate the overall essentials of the invention and that within its scope it is possible to develop a wide range of additional binary information transfer devices founded on the same basic conception.

The drawings illustrate a few prominent design examples concerned with the invention, together with a number of variation possibilities.

The following are illustrated:

FIG. 1. Basic device for the transfer of binary information in accordance with the invention involved here.

FIG. 2. A critical curve characterizing the switching behavior of magnetic thin film elements in the preferred mode of employment in this invention.

FIG. 3. An information transfer device design based on simplified geometrical assumptions.

FIG. 4. An auxiliary sketch for the qualitative determination of the induced voltages in the coupling lines, with respect to the switchover direction of the magnetization vector of a magnetic film element.

FIG. 5. An auxiliary sketch for defining the direction of current flow in the coupling lines.

FIGS. 6a and 7a. Change with respect to time of the magnetic flux during the switchover of the magnetization vector with relation to two coupling lines having geometrically different arrangements.

FIGS. 6b and 7b. Characteristic with respect to time of the induction current in two coupling lines having geometrically different arrangements.

FIG. 8. The signal to noise ratio of the induction currents flowing in the coupling lines, with respect to the geometrical arrangement.

FIG. 9. The influence of the resultant magnetic control field during the transfer of information to a controlled magnetic film element; plotted with the aid of the critical curve diagram.

FIGS. 10a to 10d. Various possibilities of arranging driver and coupling lines to compensate any possible stray flux couplings.

FIG. 11. A first design arrangement of a shift register.

FIG. 12. A first switching program for the driving currents for the achievement of a stepwise progressive transfer of information in the shift register shown in FIG. 11.

FIG. 13. A second switching program for the operation of the shift register shown in FIG. 11.

FIG. 14. A second shift register arrangement.

FIG. 15. A switching arrangement of magnetic film elements for the technical realization of the logical connectives of Boolean algebra with two input variables, in particular the conjunction and the disjunction. This arrangement is taken from one of many possibilities.

FIGS. 16 to 19. Various switching programs for the operation of the logical switching arrangement shown in FIG. 15.

FIGS. ZOa/f to 23a/f. A number of arrangements for the realization of logical connectives with two input variables.

FIGS. 23a/d to 27a/d. Various configurations for the transfer of information from a controlling to a controlled element, particularly for achieving the negation of a variable.

FIGS. 28a/e to 35a/ e. Further arrangement possibilities or coupling configurations for the achievement of logical connectives with two input variables X and Y, particularly the logical functions X'Y, XvY, Y, YVY, X-Y, XVY, and. i-Y, YVY.

FIG. 36. A two-stage coupling configuration of a logical pyramid which, in relationship to the selected switching program, performs either the AND-OR or the OR-AND connective.

FIGS. 37 to 40. Switching program for the driving currents for operating two-stage coupling configurations.

FIG. 41. A two-stage coupling configuration for the realization of the equivalence and the disvalence (exclusive OR).

FIG. 42. A two-stage coupling configuration which performs the function of a halfadder.

FIGS. 43 and 44. Switching programs for two driver lines for operating two-stage coupling configurations whereby, for the stepwise transmission of information, two superposed drive fields are used in order toachieve a synchronization-independent mode of operation.

FIG. 45. A shift-register arrangement having a synchronization-independent switching program.

FIG. 46. A synchronization-independent switching program for the operation of the shift register illustrated in FIG. 45.

By way of introduction, reference is made to the basic arrangement illustrated in FIG. 1 for the transfer of binary information in accordance with the invention involved here. As an example, this device is shown in a form which is technologically simple to manufacture, e.g. by the evaporation of various layers, one above the other. All the information transfer devices described subsequently, such as shift registers and logical circuits are based on the fundamental arrangement shown in FIG. 1.

On a substrate, for example of glass, there is a conducting metal film 1, which can be of silver, copper, aluminum or any other electrically conducting material. Over this, there is a thin layer of insulating material, this is deposited (for example) by the evaporation of silicon monoxide. Such layers of insulation tnust naturally also be provided between the evaporated conducting layers of the transfer device; in the remainder of this description it is taken for granted that they are provided, and no special reference will be made to them, either in the text or in the drawings.

Two switching elements, 2 and 3, of thin magnetic layers with uniaxial anisotropy are located on the metal film 1 and separated from it by an insulating layer. Each of these elements has a preferred direction of magnetization. Their easy direction is designated by E.

The two elements 2 and 3 are coupled inductively by means of a strip-line type coupling 4. This coupling 4 is situated above elements 2 and 3 and is separated from them by a thin layer of insulation. Two ends, 5 and'6, of the strip-line type coupling 4 are connected conductively with the metal film 1, so as to form-in conjunction with metal film 1-a coupling loop for the elements 2 and 3.

Uppermost on the device, a st-riptype driver line 7 and a strip-type driver line 8 are provided; which are also separated from coupling 4 situated underneath by an insulating layer.

If an electric current is passed through a driver line, a magnetic field H builds up; its field lines are perpendicular to the direction of the current, i.e. vertical to an axis R of the driver line. The direction of the magnetic field H with respect to the direction of the current is determined by means of the corkscrew rule.

This magnetic field H influences the switching element 2 or 3 within its range of influence and situated beneath the driver line, and causes a rotation of the magnetization, i.e. of magnetization vector M which, without magnetic field H is in the easy direction E, in the direction of the external field H.

The resulting deviation of the magnetization vector M under the influence of the external field H is now explained with the aid of a critical curve 10 illustrated in FIG. 2.

The critical curve 10 describes an astroid, which, mathematically is further described by an equation In this equation, H and H are the components of the magnetic field H in the easy or in the hard direction, and H; the anisotropy field strength. With the critical curve E=K. sin 0 (2) whereby K refers to the anisotropy constant. Without any additional amounts of energy, the requirement for minimum energy leads to angles 0:0 or O for the position of the magnetization vector M. This corresponds to the two possible stable positions 0 and 180 of the magnetization vector M in the easy direction when there is no external magnetic field.

However, there is an additional energy term, when an external field H is present in the plane of the layer:

E :H M cos O-H M sin 0 (3) in which M represents the amount of magnetization, O the angle between the magnetization vector and the easy direction, H and H the components of the external field in the easy and hard direction.

The requirement for the minimum of the total energy 1 n is calculated from the derivative With respect to the angle 0:

dE d(E +E Evaluating Equation 5 and using Equations 2 and 3 we obtain:

Hy 2 5 sin 0 cos O M "Hk (6) The quantity is usually called the anisotropy field strength. For the thin magnetic films in use today, H is of the order of magnitude of 5 oersteds.

For a given angle 0 the Equation 6 represents a straight line in the H /H plane. For a straight line 11 in FIG. 2, for example, the angle 0 is 30 and Equation 6 becomes:

This straight line 11 intersects the H =axis at 0, SH the H =axis at 0, 865H Every point (H H on the line represents an externally supplied magnetic field H, with the components H and H in the easy and hard direction, respectively, for which the magnetization vector M of the layer adjusts itself under the same angle 0 with respect to the easy direction, provided (as will be demonstrated below) there is a steady state of equilibrium. Since the slope of this line is tg 0 this allows to graphically construct the deviation of the magnetization vector. For every straight line defined by Equation 6 there are two energetic states of equilibrium: a stable and an unstable state. They ditfer by the value of the second derivative of Equation 4 according to the angle 0. The energetic stable state of equilibrium is determined by:

and the energetic unstable state of equilibrium by:

For the previously selected example the critical point can be evaluated on curve 11, Which was determined from Equation 7, when the second derivative 11 is taken as the second determining equation, is equated to zero and O is made to equal 30". The relationship is then obtained. Calculated from the Equations 7 and 12, the coordinates for the critical point for the chosen example O =30 are:

This point lies on the critical curve 10 and characterizes the point of transition from the stable to the unstable energetic state of equilibrium for a definite external field H or its components H and H (13).

In general, the critical curve 10 is the geometrical location of all critical points for any angle 0. The determining Equation 1 for the critical curve can be determined from the Equations 6 and 11, with the latter equated to zero, provided the angle 0 is eliminated from them both. From the theory of envelopes it can be proved, finally, that every equilibrium curve furnished by the determining Equation 6 represents a tangent on the critical curve, intersection being at the critical point.

Thus the direction of the magnetization vector M for a desired magnetic field H can be determined from the critical curve quite generally by plotting the H vector from the origin of the coordinates and drawing from the tip of the H vector the tangent on the critical curve. This tangent characterizes the direction of deviation of the magnetization vector M of the layer, deflected from the easy direction by the supplied external field H.

Observation of the critical curve illustrated in FIG. 2 will show that one or two stable states of equilibrium for M are available, in relationship to the position of the tip of an H vector with respect to the critical curve. If the tip of an H vector 12 is outside the critical curve, it is possible to draw only one tangent 13 on the critical curve, representing a stable energetic balance, so that there is only one stable state of equilibrium for M, which is indicated by its direction. If the tip of an H vector 14 is within the critical curve, it is possible to draw two tangents and 16 on the critical curve, representing stable energetic balance, so that there are two stable states of equilibrium for M, which are indicated by their directions. If, by extending the field, the tip of an H vector extends beyond the critical curve, the second state of equilibrium which existed previously, disappears; this disappearance is accompanied by an instantaneous switching of M into the new direction.

Reference is now made again to FIG. 1 in order to define some geometrical characteristics of the information transfer device. We regard the magnetic thin film element 2 as the controlling element, and the magnetic thin film element 3 as the controlled element. Thus coupling line 4 is an output line for element 2 and an input line for element 3. For a general case, the easy direction E2 of element 2, the easy direction E3 of element 3, the axis R7 of driver line 7, the axis R8 of driver line 8, the axis R4/2 of the output line of element 2 and the axis R4/3 of the input line of element 3, can assume various directions with respect to each other. It is preferable, however, for the axis R7 and R8 of the driver lines 7 and 8 to be parallel. With reference to these axes, the following angles are defined, which are counted positively in a counterclockwise direction.

The angle between the axis of a driver line and the easy direction is identified by s, the angle between the axis of a driver line and the axis of an output line by a and the angle between the axis of a driver line and the axis of an input line by ,8. The following angles are therefore encountered in FIG. 1:

ot7/4 is the angle between the driver line '7 and coupling line 4, regarded as output line,

[38/4- is the angle between the driver line 8 and coupling line 4, regarded as input line,

e7/Z is the angle between the driver line 7 and the easy direction of the magnetic thin film element 2,

e8/ 3 is the angle between the driver line 8 and the easy direction of the magnetic thin film element 3.

For easier understanding and a better overall conception of the conditions covering the transfer of binary information from a first magnetic thin film element to a second, under the influence of various geometrical coupling configurations, reference is made to the FIG. 3 in which a conducting metal layer 11 is provided with magnetic thin film elements 12, 13 and 23 which are insulated therefrom. The elements 12 and 13 are coupled together by a coupling line 14 located above them; the elements 12 and 23 are coupled together by a coupling line 24 located above them which is also electrically insulated from line 14 at the point where it crosses. Fronts 15, 16 and 25, 26 of lines 14 and 24, respectively, are conductively connected with the metal layer 11. Two driver lines 17 and 18 are also provided which are positioned uppermost on the device.

The two following geometrical simplifications are employed: The axes of the driver lines 17 and 18 are parallel; the easy direction E in all three magnetic thin film elements is parallel to the axis of the driver lines, i.e. the following is valid:

e17/12=e18/13=618/23=0 The axes of the couplings 14 and 24 are inclined 45 with respect to the axes of the driver lines 17 and 18, i.e. the following is valid:

The magnetic thin film element 12 behaves as a controlling element; the magnetic thin film elements 13 and 23 are the controlled elements. In the magnetic thin film elements, a stored l is defined by a magnetization vector M oriented to the right, and a stored 0 by a magnetization vector oriented to the left. Its position of rest or its initial position coincides with the easy direction.

As an example it is proposed to consider the case of transferring 1 stored in the controlling element 1 2. In order to achieve this, the first step is to deflect in the hard direction the magnetization vector of the controlled elements 13 and 23 (referred to from now on as M13 and M23) by means of a current flowing through the driver 'line 18. A driving current oriented towards the right (designated positive by definition) generates with respect to the elements under the driver lines, in accordance with the corkscrew rule, a magnetic field which is perpendicular to the axis of the driver line, directed upwards. A driving current oriented towards the left (designated negative :by definition) generates a magnetic field perpendicular to the axis of the driver line, directed downwards. For the purpose of this example, it is not important for the controlled elements 13 and 23 whether their magnetization vectors are deflected in the hard direction by a positive or negative driving current. It is prefer- 

1. IN AN INFORMATION TRANSFER CIRCUIT, A CONTROLLING AND A CONTROL MAGNETIC THIN FILM ELEMENT, EACH SAID ELEMENT EXHIBITING AN EASY DIRECTION OF REMANENT MAGNETIZATION AND A HARD DIRECTION OF MAGNETIZATION, MEANS APPLYING A FIELD TO SAID CONTROLLING ELEMENT FOR DEFLECTING THE MAGNETIZATION THEREOF AWAY FROM THE EASY DIRECTION, AND MEANS COUPLING BOTH SAID CONTROLLING AND CONTROL ELEMENTS WHOSE EFFECTIVE SIGNAL PICK-UP RANGE WITH RESPECT TO THE CONTROLLING ELEMENT IS A MAXIMUN IN A DIRECTION WHICH IS OBLIQUE TO THE DIRECTION OF SAID APPLIED FIELD AND COUPLES SAID CONTROLLING ELEMENT AT AN ANGLE BETWEEN 15 AND 75 DEGREES WITH RESPECT TO THE DIRECTION OF SAID APPLIED FIELD. 